Method of treating the rock, aplite



Patented Jan. 30, 1945 METHOD OF TREATING THE ROCK, APIJTE Ralph F. Brenner, Lancaster, Ohio, assignor to Dominion Minerals, Incorporated, Washington, D. 0., a corporation of Virginia No Drawing. Application June 11, 1941, Serial No. 397,599

1 Claim.

My invention relates to a method of treating the rock, aplite. It has to do, more particularly, with a method of treating aplite preparatory to grinding.

Aplite is a rock product, commercially mined chiefly in Virginia. It is composed of several minerals in the following approximate amounts:

Per cent Zoisite 23 Albite 55 'Iitanite, apatite and clino-zoisite 2 Quartz 2 Sericite l3. Microcline 5 At the present time, considerable difiiculty is encountered in grinding the rock aplite due to its excessive hardness, the nature of its cleavage, and the tendency to produce an excessive amount of fines during grinding. In grinding aplite at the present time, a large amountpf fines, finer than 200 mesh, are produced because of the nature of the grinding action required to reduce the extremely hard lumps into grains of suitable size. It has been found in actualpractice that about 40 to 45% of extreme fines are produced in the grinding operation. Due to the nature of these fines, a large percentage of this material is waste material. Also, because of the extreme hardness and nature of the cleavage of the aplite, it is necessary to have very rugged and wearresistant grinding equipment, which is expensive, and still excessive wear occurs.

As indicated in the co-pending application of Ralph F. Brenner and Roger D. Dubble, serial 1 No. 368,694, new Patent No. 2,304,440, filed December 5, 1940, the rock aplite has iron in combined form therein, usually present in the mineral zoisite, and it is very desirable to reduce this iron content in order to make the aplite suitable for use in glass batches or for similar uses.

One of the objects of my invention is to treat the rock aplite before grinding in such a manner that its hardness will be reduced, the nature of its cleavage will be changed and, therefore, grinding will be facilitated.

Another object of my invention is to treat the rock aplite before grinding in such a manner that grinding will not only be facilitated but also subsequent treatment to remove the iron content will be facilitated.

Another object of my invention is to treat the rock aplite before grinding in such a manner that excessive wear on the grinding equipment will be reduced to a minimum.

Another object of my invention is to treat the rock aplite in such a manner before grinding that its hardness will be greatly reduced and the nature of its cleavage changed so that the grinding operation required to reduce the lumps of aplite to suitable grain size will not be of such a nature as to produce a high percentage of fines.

Another object of my invention is to provide a complete and eflicient process for treating the rock aplite, as mined, to reduce it to the proper grain size and to reduce the iron content thereof.

The rock aplite, as mined, usually consists of lumps of various sizes. As previously indicated, it has been very diflicult to grind these lumps in order to produce grains of the proper size. I have found that if the aplite is subjected to a proper calcining or heat-treating operation before grinding, grinding is facilitated. I have discovered that for this purpose it is desirable to heat-treat the aplite at a temperature in excess of 1000 F. Temperatures varying from 1000 to 2500 F. have been employed by me with success in this heating operation but I prefer to use a temperature ranging from 1500 to 2100 F. The time of heating will depend upon the size of the lumps of the aplite. It is merely necessary to heat the aplite for a period sufficient for the heat to penetrate completely into the interior of the lumps. After the aplite is subjected to this heat-treatment, it is cooled in air or waterquenched or sprayed. I prefer to either waterquench or spray the aplite.

The calcining or heat-treating operation apparently breaks down some of the minerals which impart the extreme hardness to the aplite. This is especially true of the mineral zoisite which constitutes about 22% of the aplite. Furthermore, the nature of the cleavage of the aplite is changed in such a manner that crushing or grinding is facilitated. Apparently, the mineral zoisite, and perhaps other minerals, acts as a bonding agent between the cleavage planes and the heating operation breaks down this mineral bonding agent.

I have discovered that after the calcining operation described above, the aplite is softer and the nature of its cleavage changed so that it can be ground to suitable screen sizes with greater ease and without producing excessive fines.

In making certain tests with reference to this invention, I took lumps of aplite, from two to three inches in diameter, and calcined the aplite at a temperature of about 1750 F. for a period of 30 minutes. Part of these lumps were then quenched in water and the other part was cooled in air. I then selected samples of the untreated aplite, samples of the treated and quenched aplite and samples of the treated and air-cooled aplite and made crushing tests on these various samples. Great difliculty was encountered in crushing the untreated aplite. n the other hand, the treated and air-cooled aplite crushed easily and the treated and quenched aplite even more easily. These crushing tests indicated that the trea'ted aplite is not only softer than the untreated aplite but also that the nature of its cleavage is changed considerably and in such a manner that crushing is facilitated.

In further tests relative to this invention, samples of the untreated aplite and samples of aplite treated in the manner indicated above'and waterquenched were ground in such a manner that all particles would pass through a iii-mesh screen. It was found that in the case of the untreated ground aplite 38% of the ground material passed through a ZOO-mesh screen, or in other words, 38% of the material was in the form of excessive fines. On the other hand, in the case of the treated water-quenched aplite, only 5% of the ground material passed through a 200-mesh screen. This, obviously, definitely indicates that the production of fines during grinding is reduced to a minimum by the heat-treating operation.

After the aplite is reduced to the proper grain size, it may be subjected to the acid treatment described in said Patent No. 2,304,440 in order to reduce the iron content. The acid treatment is facilitated by the prior calcining and grinding operations. The prior calcining operation apparently breaks down the insoluble iron in combined form in the aplite, such as in the mineral zoisite, and renders it soluble in acids. After the acid treatment, the aplite is washed to remove 4 the iron salts and excess acid therefrom as described in said application.

It will be apparent from the above description that I have provided an eflective process for treating aplite before it is ground in such a manner that its hardness will be reduced considerably and the nature of its cleavage will be changed so that grinding, without the production of excessive fines, will be facilitated. The cost of the grinding operation will be reduced considerably and waste material produced during the grinding operation will be reduced to a minimum. Furthermore, excessive wear on the grinding equipment will 'be reduced to a minimum. Also, the calcining or heat-treating operation prior to grinding will facilitate the subsequent acid treatment to remove the iron therefrom.

Various other advantages will be apparent from the preceding description and the following claim.

Having thus described my invention, what I claim is:

The process of treating aplite in lump form to facilitate reduction thereof to the proper particle size suitable for use in ceramic ware with the production of a minimum amount of fines which will pass through a 200-mesh screen during grinding and to facilitate removal of iron, which comprises heating the aplite in lump form at a temperature ranging approximately from 1000 to 2500 F. for a period sufficient to cause the heat to penetrate thoroughly into the lumps to break down some of the minerals which impart the extreme hardness and the nature of its cleav.

age thereto, and then grinding the lump aplite to the desired particle size suitable for use in ceramic ware and treating the aplite after grinding with an acid to dissolve the soluble iron compounds and then washing the aplite to remove the iron salts so produced and the excess acid.

RALPH F. BRENNER. 

